This invention relates to drive for vehicles, and more particularly to a fluid drive system for providing steering of a track-type vehicle.
In the use of a track-type vehicle, it is of course important that effective driving of the vehicle in a straight direction take place. Furthermore, it will be understood that effective steering of the vehicle, in either the forward or reverse direction of vehicle drive, must be accomplished. Generally, it is well known to provide two separate hydrostatic motor units for driving the wheels or tracks on the respective sides of the vehicle. Such a system is disclosed in U.S. Pat. No. 3,655,004. It will be understood that it would be advantageous to provide a system wherein a single pump can be used to provide proper driving and actuation for steering of wheels or tracks of a vehicle.
U.S. Pat. No. 2,560,554 discloses a drive system wherein shafts can be locked relatively together to drive a vehicle through planetary drive systems. Such shafts can also be made to rotate in opposite directions to provide a steering effect. It is to be seen in such patent that a relatively complicated electrical and mechanical system is used for providing such steering effect of the vehicle.
U.S. Pat. No. 3,672,167 discloses a hydrostatic transmission and a motor which is used to drive a differential for driving a pair of wheels. However, there is no steering system disclosed therein.
U.S. Pat. No. 3,782,488 discloses a pair of hydrostatic transmissions with a single control for controlling the displacement of a pair of pumps to achieve a steering effect. Thus, similar to U.S. Pat. No. 3,655,004, a pair of pumps are used in the operation of the system.